Slab inductor device providing efficient on-chip supply voltage conversion and regulation

ABSTRACT

A voltage conversion circuit such as a buck regulator circuit has a plurality of switches coupled to a voltage source; a slab inductor having a length, a width and a thickness, where the slab inductor is coupled between the plurality of switches and a load and carries a load current during operation of the plurality of switches. The voltage conversion circuit can also include means to reduce or cancel a detrimental effect of other wires on same chip, such as a power grid, that conduct a return current and thereby degrading the functionality of this slab inductor. In one embodiment the wires can be moved further away from the slab inductor and in another embodiment magnetic materials can be used to shield the slab inductor from at least one such interfering conductor.

TECHNICAL FIELD

The exemplary embodiments of this invention relate generally to powersupplies and more specifically to switching-type power supplies such asswitching-type voltage conversion circuits and regulator circuits thatcan be formed in an integrated circuit.

BACKGROUND

Power consumption is an important consideration for current and futureserver and other processor designs. A power delivery network has severalstages, each ideally having the maximal possible power conversionefficiency from the external AC mains supply plug to a processorinternal power grid back-end-of-line (BEOL) network. An important linkin this power delivery network is the last stage from the external dataprocessor package power connection pins to an internal BEOL power grid.The power grid may be considered as a power distribution network that isfabricated within the processor chip or component. A current trend is toincrease processor power consumption while decreasing the supplyvoltage. This can result in a very large electrical current beingrequired in the last critical stage of the power supply chain and canresult in issues such as, for example, the generation of power supplynoise and/or simply the inability to withstand the high required currentin the connections. One approach to addressing these issues is to designa further voltage conversion chip(s) within the processor package, or tohave a monolithic voltage conversion unit on the same processor chip,thereby allowing a higher input voltage to the chip and thereby reducingthe supply current.

The Buck regulator is a step-down type of voltage conversion unit thatcan be used in integrated circuit (chip) applications.

SUMMARY

In a first aspect thereof the exemplary embodiments of this inventionprovide a voltage conversion circuit that comprises a plurality ofswitches coupled to a voltage source; and a slab inductor having alength, a width and a thickness, the slab inductor being coupled betweenthe plurality of switches and a load and carrying a load current duringoperation of the plurality of switches; where the slab inductor iscoupled to the load through a power grid that comprises at least oneconductor, and where the power grid has an aperture made therein thatunderlies a location where the slab inductor is disposed above the powergrid.

In another aspect thereof the exemplary embodiments of this inventionprovide a voltage conversion circuit that comprises a plurality ofswitches coupled to a voltage source; a slab inductor having a length, awidth and a thickness, the slab inductor being coupled between theplurality of switches and a load and carrying a load current duringoperation of the plurality of switches; and a magnetic shield configuredto shield the slab inductor from at least one conductor carrying areturn current.

In another aspect thereof the exemplary embodiments of this inventionprovide a voltage conversion circuit that comprises, disposed within anintegrated circuit, a plurality of switches coupled to a voltage source;and a slab inductor having a length, a width and a thickness, the slabinductor being coupled between the plurality of switches and a load andcarrying a load current during operation of the plurality of switches.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is an enlarged top view of an open slab inductor in accordancewith this invention.

FIG. 1B, taken across the section line B-B of FIG. 1A, is an enlargedcross-sectional view of the open slab inductor. The slab inductor shownin FIGS. 1A and 1B, and other Figures, is not drawn to scale.

FIG. 1C shows that a return current impact caused by the power grid ofthe same chip which can be reduced or eliminated by embedding the openslab inductor in a magnetic shielding layer. Note that the power grid isa most common example of an interfering conductor which may impact theopen slab inductor unless properly located or shielded, but is not theonly case covered by this invention, for example the magnetic shieldinglayer can protect the slab inductor from another wire running close toor adjacent to the slab inductor.

FIG. 1D shows in cross-section an embodiment where the power grid has atleast one opening or window or aperture that is designed to lie beneaththe location of the slab inductor thereby eliminating or at leastreducing coupling between the slab inductor and the power grid.

FIG. 1E shows an alternative embodiment of the embodiment shown in FIG.1D where metal stripes (metal conductors), which are a part of the powergrid, are located orthogonal to the length of the slab inductor. Thosestripes that would run collinear with the length of the slab inductorare removed (e.g., not fabricated by design). The stripes serve toshield the slab inductor from the silicon substrate and also serve topreserve the integrity of the power grid by maintaining equal potentialacross the power grid as required.

FIG. 2A illustrates an exemplary embodiment wherein a return currentimpact can be reduced or eliminated by disposing the open slab inductorover (or under—such in FIG. 2D) a magnetic shielding layer.

FIG. 2B shows an exemplary embodiment wherein the magnetic shieldinglayer is implemented as a pattern of stripes in a ferromagnetic layerbetween the open slab inductor and a power grid. These stripes caneither be narrow and dense as shown, or can be another division of themagnetic layer into rectangles of much different aspect ratio.

FIG. 2C shows an exemplary embodiment wherein the magnetic shieldinglayer 40 is implemented as a multi-layered laminated structure, witheach layer separated from the next by a thin layer of oxide or someother electrically insulating material. A combination of both slotting(FIG. 2B) and lamination (FIG. 2C) can be one preferred embodiment ofthis invention.

FIG. 2D shows an embodiment where a separate continuous layer orpatterned layer and/or laminated magnetic shielding layer can disposedon an opposite side of the open slab inductor in order to mitigate anyreturn current issues resulting from any metallization in the chip abovethe slab or in the chip package or external to the chip package, as wellas to reduce or eliminate potential EMI caused by radiation emitted fromthe slab inductor.

FIG. 2E shows an embodiment where the slab inductor is comprised of twoor more electrically connected sub-slabs. This embodiment may bepreferred due to current limitations related to fabrication of a thickcopper conductor.

FIG. 3 depicts an exemplary Buck regulator circuit that can be utilizedto implement the exemplary embodiments of this invention. One or morephases of such circuits with corresponding slab inductors operating inparallel for driving current to the same load may be implemented.

FIG. 4 is a chart that summarizes exemplary circuit simulation resultsof the circuit shown in FIG. 3 for a case where D+E=1 (inductor currentreturns to zero at each cycle) at a frequency of 200 MHz, when varyingthe duty cycle D at a constant load resistance.

DETAILED DESCRIPTION

As will be made apparent below the embodiments of this invention may beimplemented as part of a Buck Regulator, or as part of anyconversion/regulation design which contains inductors. The invention canalso be implemented as part of a Boost regulator, which is a step-uptype of voltage conversion unit. The invention can be implemented aspart of an integrated circuit chip by including a slab inductor asdescribed below.

In that conductors existing on the same chip may interfere with theproper operation of the slab inductor (often by the return current thatthey carry serving to reduce its inductance and its correspondingquality factor) the exemplary embodiments provide at least two solutionsto this problem: (a) move any conductors near to or adjacent to theslab, such as by creating a window or aperture in a chip power grid thatcarries a return current and/or (b) adding ferromagnetic material(magnetic material in short) to magnetically shield the slab inductorfrom at least one conductor carrying a return current.

In a multi-core processor architecture, as well as other applications,the use of the embodiments of this invention enables the provisioning ofindependent and efficient voltage conversion and regulation to separateprocessor cores which, in turn, can beneficially reduce processor energyconsumption, known in the art as DVFS (Dynamic Voltage and FrequencyScaling).

By way of background there are currently three main voltage conversionapproaches on-chip: linear regulation, switched capacitor conversion,and inductor-based conversion/regulation. Linear regulation is basicallyequivalent to having a series resistance on-chip to reduce the voltageand is therefore non-efficient due at least to resistive losses.Switched capacitor circuits have low efficiency unless working in apredefined and fixed voltage conversion ratio and are thus mostefficient only for specific and fixed voltage conversion ratios (e.g., a2:1 ratio). Inductor based designs, such as Buck circuits (Buckregulators), allow for both voltage conversion and regulation on-chip byproviding a continuous efficient output voltage range. However,conventional on-chip inductor based designs suffer from low powerconversion efficiency (e.g., about 70%-75% at most) due at least in partto the low quality factor (Q) of existing on-chip inductor technology(e.g., Q<7).

The various exemplary embodiments of this invention enable on-chip >90%voltage conversion efficiency and regulation efficiency that is enabledat least in part by a novel on-chip open slab inductor device.

The exemplary embodiments of this invention provide a flat >90%efficient, fully on-chip regulator design, such as but not limited to aBuck regulator design, that can be used with, for example, aV_(supply)=1.35V, 0.7V<V_(load)<1.25 V, I_(load)˜100 A. The exemplaryBuck regulator design uses what can be referred to as “open slabinductor” embodiments that are made possible by this invention.

The exemplary embodiments of this invention provide the use of what maybe referred to as a partially or fully “air core” inductor, which caninclude an inductor coupled with and embedded within a low permeabilitymedium and/or an inductor coupled with at least one layer of magneticshielding (e.g., ferromagnetic) material disposed between the inductorand potential return current paths.

The exemplary embodiments of this invention provide for the use of arelatively wide and thick metal (e.g., copper) inductor slab crosssectional area to reduce resistive losses, increase electricalconductivity and thus allow for high Q factors (e.g., as much as 30 andgreater).

The exemplary embodiments of this invention also provide for the use ofmagnetic material(s) only for magnetic shielding of the open slabinductor device from return current paths, such as those represented byan on-chip power grid and/or other nearby BEOL wires (conductors), aswell as possibly package-related metallization and/or other metalobjects in the vicinity of the chip.

Another exemplary embodiment of this invention reduces the detrimentaleffect of other nearby on-chip wires by locating them far away from theslab and creating an aperture in the power grid, as will be describedbelow with reference to FIGS. 1D and 1E.

Some conventional approaches use magnetic core inductors in which thereis no intentional air gap in the magnetic flux path, thereby requiringmost of the magnetic energy to be stored within the magnetic material.While this may tend to increase the inductance, it also serves todecrease the quality factor (Q), where Q is the main figure of merit ofthe on-chip inductor and is directly related to the maximum obtainablepower conversion efficiency. The quality factor obtained by theseconventional approaches is reduced at least in part due to eddy currentlosses in the magnetic material in addition to other magnetic lossessuch as domain rotation. These eddy current losses tend to be high sincemost of the magnetic energy is stored within the magnetic materialitself.

Contrary to these conventional approaches, the use of the open slabinductor device of this invention stores most of the magnetic energy inair (or in a dielectric medium) and relatively little energy in themagnetic material. This allows for a much higher electrical currentdensity in the metal (e.g., copper) slab before reaching magnetic fieldsaturation in the given magnetic material. Since the total requiredon-chip inductance is inversely proportional to the needed loadelectrical current, it is possible to obtain the required inductance forthe given required high load current while optimizing the quality factorand the resulting power conversion efficiency. A high metalcross-sectional area in the slab is a desirable goal in order to achievea high quality factor.

A primary purpose of the magnetic materials that are used in the contextof this invention is to magnetically shield the Open Slab InductorDevice from other current carrying (e.g., metal) wires on-chip whichwould otherwise act as current return paths, thereby reducing thequality factor Q of the slab often by as much as an order of magnitudeor more. Some most detrimental metal wires on chip (in this context) arethe processor power grid wires. The magnetic shielding used as an aspectof this invention for the open slab inductor device also serve to cancelcrosstalk between the open slab inductor device and the processor globalclock distribution network (or other sensitive wires on-chip), which canbe reduced by other engineering means for an embodiment where themagnetic layer does not exist, such as in the embodiments shown in FIGS.1D and 1E.

In practice, the open slab inductor device includes a wide and thickmetal (such as copper) BEOL wire in a high metal layer of the metalstack which forms the inductor of the voltage conversion/regulationcircuit. Regulation can be performed from the (external to chip) supplyof, e.g., 1.5 V (or lower) to a continuous range of output voltages(e.g., about 1.4 V down to about 0.6 V). Another embodiment option is afixed ratio voltage conversion (2:1 and the like), or one circuitcombining both conversion and regulation (either by the same Buckcircuit or in two consecutive circuits performing fixed conversion firstfollowed by regulation).

Some (typically most often preferred) embodiments include several phasedopen slab inductor devices which operate together in parallel as acircuit to supply the required load current. Some embodiments use onesuch multi-open slab inductor device circuit for each processor coreseparately, other embodiments use more than one multi-open slab inductordevice circuits in parallel for each processor core separately. However,it is also within the scope of this invention to use one open slabinductor device circuit to supply power to two or more processor cores(or other circuitry).

The magnetic shielding can be achieved by at least two differentapproaches: One approach is to immerse the open slab inductor within alow permeability (e.g., about 10-15 or even less) and high resistivitymagnetic material medium (as opposed to the conventional use of veryhigh permeability materials of, for example, about 1000 which are alsohighly conductive). A second approach is to use a high permeabilitymagnetic material layer between the open slab inductor device and thepower grid, which acts as a “perfect H” magnetic shielding layer. Inorder to further reduce the magnetic losses within this magnetic layerthe layer can be laminated (FIG. 2C—wherein multiple magnetic shieldinglayers are separated by thin insulating layers) or patterned so as tohave openings within it (FIG. 2B), or even more preferably bothapproaches can be used together. One example is to use a slotted layercharacterized by narrow rectangular regions (although other geometricshapes could be used as well such as rectangles with different aspectratios) which prevent eddy currents from forming within the magneticlayer (such eddy currents are the main contributors to the magneticmaterial loss), plus aiding to form an improved aspect ratio of themagnetic layer which yields a higher effective permeability. Thelamination of the magnetic shielding is beneficial since it alsoimproves the magnetic properties of the layer (e.g., it reduces an “edgecurling effect” which tends to reduce the effective permeability of themagnetic layer).

Both of the embodiments of this invention shown in FIGS. 2B and 2Cachieve the same purpose of providing magnetic shielding and alsoincreasing the quality factor.

As was noted above, a further embodiment combines the slotted andlaminated magnetic layer embodiments to provide a slotted and laminatedmagnetic shielding layer.

In another embodiment a second magnetic shielding layer can be providedover the top of the open slab inductor device, thereby forming a secondmagnetic shield between the open slab inductor and the top of theintegrated circuit (IC) package. The top of the IC package may have ametal cover (which could support eddy currents and reduce the qualityfactor by both reducing the inductance and creating losses). The use ofthis embodiment can thus be contingent on the type of packaging that isused to house the processor cores and/or other circuitry of interest.Another benefit that can be realized by the use of the second topmagnetic shielding layer is the avoidance of EMI (electro-magneticinterference) that may radiate from the top surface of the package dueto operation of the open slab inductor device.

While the embodiments of this invention will be further described belowin the context of a switching converter circuit embodied as a Buckconverter (regulator) circuit that contains the open slab inductordevice to provide voltage conversion and regulation, it should beappreciated that other inductor-based voltage conversion circuits, suchas boost converters, can also be used.

The Buck converter circuit that uses the open slab inductor device canprovide, in one non-limiting example, an on-chip supply regulation(dynamic voltage frequency scaling (DVFS)) of:

-   about 1.35 Volt (supply) to a range of about 0.7 to about 1.25    regulated Volts;-   about a 90% power efficiency over the entire output voltage range    (i.e., the efficiency is basically “flat” over the output voltage    range); and-   >10 Amper/mm² current density or higher.

In contrast, conventional approaches based on a closed yoke design canprovide only about a 75% peak efficiency at lower load currents, wherethe quality factor is severely limited by magnetic material conductance.Only relatively very low current densities are possible to avoid high μmagnetic material saturation. In these approaches larger wire widths arenot beneficial since most of the losses are magnetic material losses.

The use of the embodiments of this invention avoids the high magneticmaterial losses (e.g., about 15% in the closed yoke approach) due mainlyto eddy current losses that can limit the Q to non-optimum values (e.g.,less than 10). Note that magnetic rotation and domain wall movementlosses are also proportionally reduced when replacing a closed yoke withthe open slab structure that is an aspect of this invention.

The exemplary embodiments of this invention are more correctly focusedon current density as a figure of merit as opposed to inductance densityas in various conventional approaches. The inductance density can beshown to be a misleading figure of merit as follows.

Unlike in switched capacitor circuits (a different approach for on-chipvoltage conversion) in which the total required floating capacitance isproportional to the load current and power, in a Buck converterregulator the total required inductance is inversely proportional to theload current and power:

L(ΔI/Δt)=V_(S)−V_(L)=>L*ΔI=(V_(S)−V_(L))*Δt=constant, where V_(S) is thebuck regulator source voltage and V_(L) is the load voltage.

More precisely, for an exemplary case where V_(S)=1.35V and0.7V<VL<1.25V, for a condition where D+E=1 (inductor current waveformwhich reduces to zero once in a cycle) at V_(Lmin)=0.7V (the minimaloutput voltage corresponding to the maximal required inductance value)one obtains at V_(Lmin):

L _(min)=1/2*R _(L)*(V _(S) −V _(L))/V _(S) *T,

where D is the duty cycle (fraction of the cycle when inductor currentis increasing) and E is the fraction of the cycle when inductor currentis decreasing, so that D+E=1 denotes a condition wherein the inductorcurrent is always changing while reaching zero once in a cycle (eitherincreasing or decreasing, see the example of FIG. 3), R_(L)=V_(L)/I_(L),T=1/f

and where

L*I _(L) =V _(Lmin) /V _(S) [(V _(S) −V _(Lmin))/2f].

As an example, L*I_(L)=8.42 pH (picoHenry)*100 (Amps) at 200 MHz.

For the case of D+E=0.5 (where the inductor current is forced to zeroduring half of the cycle) one obtains L*I_(L)=4.2 pH*100 (Amps) at 100MHz.

Thus, one needs a very small total inductance at large currents whichmeans that fewer smaller inductor can be used to carry the same totallarge load current. The embodiments of this invention employ the usageof a small number of the smaller open slab inductors to carry the samelarge load current for which many closed yoke higher inductors arerequired.

Since the open slab inductor structure enables much higher Q factors(e.g., 20 . . . 30) the high magnetic coupling approach used in theclosed yoke structures is not required to separate between the DC and ACinductor currents. One non-limiting example of a preferred embodiment ofthis invention therefore employs only weakly magnetically coupled openslabs forming a multi-phase Buck converter design.

FIG. 1A is an enlarged top view of an open slab inductor 10 inaccordance with this invention while FIG. 1B, taken across the sectionline B-B of FIG. 1A, is an enlarged cross-sectional view of the openslab inductor 10. The open slab inductor 10 is characterized by having alength, a width (W) and a thickness (T). The open slab inductor 10 canbe formed of a single monolithic body of an electrical conductor such asone containing a metal, such as copper, or metals, or it can be formedas a multi-layered body of a metal or metals, such as two or more layersof copper formed one above the other. The open slab inductor 10 may becharacterized without limitation as being an inductance (openenvironment) air core device designed with a supporting structure orstructures so as to reduce or eliminate a return current impact fromadjacent conductors, such as the on-chip power grid 20 shown in FIG. 1C.

As an example, for inductor dimensions of w=200 μm, t=7 μm, length=400μm, in copper, one obtains (in open environment, namely as a partialinductance):

-   L=138.8 pH, R=5 mΩ, and-   Q=35 (at 200 MHz)=>L/R=28 nsec,

that is realizable by the air core slab inductor 10.

It should be noted that due to the high cross section area of the openslab inductor 10, the electro migration (EM) limit is ˜15 Amper per slab(in copper as an example).

Note that the relatively small area required (>10 A/mm²) can occupydedicated top metals of the chip only. In addition, control parameterscan be designed to minimize the impact of the return current, crosstalkto clock/wires and EMI.

The inductance of an open slab inductor 10 such as depicted by FIGS. 1Aand 1B may be significantly reduced in an actual implementation of achip environment due to adjacent wires on-chip carrying a return currentthereby forming a smaller inductance loop. The presence of a returncurrent reduces both the inductance and the Q factor, and has thepotential to significantly degrade the usefulness of the slab inductor10. This invention therefore provides at least two different solutionsto this problem. A first solution involves moving or re-locating thesereturn current carrying wires (conductors) as far as is practicallypossible from the open slab inductor 10. The second solution employsmagnetic shielding between the open slab inductor 10 and these returncurrent carrying wires (conductors).

The first approach of moving the disturbing (e.g., return currentcarrying) wires away from the slab inductor 10 is exemplified in FIGS.1D and 1E. These Figures demonstrate the treatment of what may beconsidered as the major set of potentially return current carrying wiresdetrimental to the open slab inductor 10 functionality, e.g., the powergrid of the same chip. FIG. 1D shows an embodiment by which an aperture20A is opened in the chip power grid 20 which eliminates the flow ofreturn current right below or close to the open slab inductor 10 withinthe power grid 20. FIG. 1E shows a modified embodiment in which at leastsome power grid wires 20B are left below and in the vicinity of the openslab inductor 10, being those which are orthogonal to the length of theopen slab inductor 10 itself, and therefore those conductors that cannotconduct a collinear return current to the excitation open slab inductorcurrent. These orthogonal conductors or stripes 20B may be required orat least desirable in some embodiments and instantiations of the powergrid design in order to maintain the integrity of the power grid 20 as alow impedance, fixed potential electrically conducting plane.

The embodiments of this invention also encompass forming magneticshielding between the open slab inductor 10 and the other wirespotentially carrying the detrimental return current, as illustrated bymeans of the non-limiting examples in FIG. 1C, FIG. 2A, FIG. 2B, FIG.2C, FIG. 2D and FIG. 2E.

These two solutions are not mutually exclusive, and both can be used insome form in the same integrated circuit package.

In one exemplary embodiment of the second solution shown in FIG. 1C thereturn current impact can be reduced or eliminated by embedding the openslab inductor 10 in a magnetic shielding layer 30, such as a layer 30comprised of a low conductivity material such as Polyimide Ferrite whichhas a magnetic relative permeability significantly larger than one. Inthis case the magnetic fields emanating from the open slab inductor 10are confined to the Polyimide Ferrite medium, and the magnetic shieldinglayer 30 thus avoids the power grid destructive effect on the inductanceof the open slab inductor 10. This resulting increase in inductance thatis realized by mitigating the return current losses serves to increasethe Q, increase the efficiency and reduce the area that is needed toimplement the inductor.

Referring to the cross-sectional view shown in FIG. 2A, in anotherexemplary embodiment of the magnetic shielding solution of thisinvention the return current impact can be reduced or eliminated bydisposing the open slab inductor 10 over (above the power grid 20) amagnetic shielding layer 40 that is preferably electrically floating (orat most tied at but one point to circuit ground). The magnetic shieldinglayer 40 is placed between the open slab inductor 10 and the underlyingpower grid 20. The magnetic shielding layer 40 can be fonned as one ormore substantially continuous layers or, more preferably, it can beformed as one or more non-continuous layers (e.g., patterned orapertured layers). Here again, the power grid 20 is presented by exampleas a most common example of an interfering conductor which may impactthe open slab inductor 10 unless properly located or shielded, but isnot the only case covered by this invention. For example the magneticshielding layer 40 can protect the slab inductor 10 from another wirerunning very close to the slab inductor 10.

Referring to the top view of FIG. 2B it can be seen that in oneexemplary embodiment the magnetic shielding layer 40 can be implementedas a pattern of stripes made in a ferromagnetic layer between the openslab inductor 10 and the power grid 20. These stripes can either bedense and close packed as shown (whereby minimizing eddy current lossesin 40) or they can resemble wider rectangles or squares or some otherpattern (thereby avoiding magnetic edge effect losses in the magneticshielding layer 40).

In some embodiments, and as is shown in the cross-sectional view of FIG.2C, it can be preferred to implement the magnetic shielding layer 40 asa multi-layered laminated structure, with each thin ferromagnetic layer42 separated from the next by a thin layer 44 of oxide or some otherelectrically insulating material for reducing the eddy current losses,or even by conductive thin layers (such as copper) which still aid inreducing or cancelling the magnetic edge curling effect.

One suitable but non-limiting material for implementing the magneticshielding layer 40 is to use a film or films of amorphous CoZrTa. Othersuitable materials can include NiFe with different composition ratios,or other compound ferromagnetic materials preferably with high magneticpermeability and with high electrical resistivity.

In general, the magnetic shielding layer 40 can be characterized asconfigured by being formed as a plurality of layers, where in oneembodiment such as in FIG. 2B the plurality of layers are disposed in asame horizontal plane located between a plane defined by the length andwidth of the slab inductor 10 and the power grid 20, and where inanother embodiment individual ones of the plurality of layers aredisposed one above another in a laminated manner as in FIG. 2C betweenthe plane defined by the length and width of the slab inductor 10 andthe power grid 20. In a still further embodiment some of the pluralityof layers are disposed in the same horizontal plane located between theplane defined by the length and width of the slab inductor 10 and thepower grid 20, and some of the plurality of layers are disposed oneabove another in a laminated manner between the plane defined by thelength and width of the slab inductor 10 and the power grid 20.

The use of the “air gap” in the magnetic flux of the open slab inductor10 increases the current density versus some conventional closedmagnetic yoke approaches, and results in a much higher current densitybefore magnetic saturation occurs.

Further, and referring to FIG. 2D, it is pointed out that a separatecontinuous layer or patterned layer and/or laminated magnetic shieldinglayer 40B can disposed on the opposite side (opposite to the power grid20) of the open slab inductor 10 in order to mitigate any return currentlosses resulting from any metallization in the top of the chip packageand/or external to the chip package and/or to other in-chip wiring thatmay lie above the slab inductor 10, as well as to reduce or eliminatepackage-generated EMI.

It should be noted that the specific geometry, number of layers, etc.,of the magnetic shielding layer 40 can be designed to differ from thespecific geometry, number of layers, etc., of the upper magneticshielding layer 40B. That is, they can be separately designed andoptimized for their intended purposes.

As a non-limiting example of an embodiment of this invention, andreferring to FIG. 2E, the open slab inductor 10 could be formed as a 200μm wide slab in two copper layers (slabs) 10A, and 10B, each having athickness of about 3 μpm (total thickness T being about 6 μm), and themagnetic shielding layer 40 can be a 2 μm thick layer with apermeability (mu)=1000, and assuming as an example zero conductivity ofthe magnetic material. The power grid 20 could be located for exampleabout 2.5 μm below the lower-most slab of the open slab inductor 10. Forthis non-limiting example one can obtain a Q of about 29.5 at 200 MHz(assuming as a non-limiting example L=360 pH with a slab length of 500μm). It can be shown that without the presence of the magnetic shieldinglayer 40 the Q would be reduced to only about 1.6.

When considering the foregoing example, but with magnetic shieldinglosses (e.g., a finite 100 μΩ-cm resistivity of the magnetic material)included and mu=1000 the value of Q is about 20.5 at 200 MHz. Note thatthe value of Q can be increased considerably when the patterned (e.g.,striped) magnetic shielding layer 40 is used, and Q can be increased aswell when the magnetic shielding layer is also laminated, which can bydesign be made practically almost to the point of the original case withno magnetic layer losses (e.g., Q˜30).

It should also be noted that beyond the exemplary embodiments of the twomain fundamental solutions (moving away the disturbing wires ormagnetically shielding them) as shown in FIGS. 1C,1D, 1E, 2A, 2B, 2C, 2Dand 2E, the examples of the embodiments of this invention include anycombination of the solutions described above. As a non-limiting example,one may form both an aperture 20A in the power grid 20 and use amagnetic shielding layer (30 or 40) in the same embodiment, therebygaining the benefits of both approaches.

During use of the exemplary embodiments of this invention, and foron-chip voltage supply regulation, several basic Buck regulator circuitsof a type shown in FIG. 3 can be used, each operating phased togetherand coupled together with the same D+E value. An overall system Q of atleast 20 may be required (e.g., at 100 MHZ-200 MHz) for obtaining thedesired high power efficiency, and several phases can be used in tandemto drive an exemplary value of 30 A per processor core output current.The series resistance losses in the combination of the transistors, viasand wires are assumed to be reasonably designed so as to be preferably,but not limited to, no more than half the losses in the slab inductors10. It is also assumed that a reasonable core decoupling capacitance isprovided that is sufficient for obtaining an exemplary value of about 15mV ripple at 100 MHz, a>10 Amper/mm² overall current density occupyingprimarily or exclusively dedicated top metal layers of a chip, and aminimum 90% efficiency at (worst case) a 0.7 Volt output. All of thesevalues are given as one non limiting example only, and the same openslab inductor concepts can be used in a large variety of inductor-basedon-chip voltage converters/regulators which are not limited to Buckconverters and may as well include boost converters, buck-boostconverters and the like, as known to a person skilled in the art.

FIG. 3 is a basic simplified circuit diagram of a non-limiting exampleof a single slab Buck regulator 50 that could be used to simulate theperformance outlined above. The Buck regulator 50 includes at least twotransistors Q1 (PMOS) and Q2 (NMOS) driven by phased frequency sourcesFS1 and FS2, respectively (in practice each of these transistors isoften implemented by a large number of transistors connected in paralleland/or multi fingered transistors as required for providing the neededload current). The transistors Q1 and Q2 are connected at Node 1 andcoupled to a first terminal T1 of the slab inductor 10. In this veryspecific and non-limiting simulated example, the slab inductor 10 isassumed to have an inductance of about 80.5 pH and an inherentresistance R1 of about 3.5 ma A second terminal (T2) of the slabinductor 10 is coupled though a via or vias (having an inherentresistance R2) and distribution wires to a decoupling capacitor Clhaving a capacitance of about 1.8 pF in this specific example. Thesecond terminal T2 is also coupled to a normalized processor core load(PCL) which is represented here as a simple resistor of 140 Ω, though inpractice one can consider the super-linear current voltage dependence ofthis type of a load. The overall wiring losses are assumed in thisspecific example to be equal to the actual transistor losses (serieschannel conductance and CV²f losses). The simulation was performed withD+E=1 at 100 MHz /200 MHz, as well as with D+E=0.5. The circuit wasscaled 1:1000, where 1 mA represents 1 A. No slab-to-slab coupling wasassumed, and the ripple was estimated by dividing a single phase resultby the number of phases (accommodating ripple cancellation effects).Note that in practice this rather crude approximation would later becorrected to account for the actual combined ripple. A 5 A load currentwas simulated in all cases at the 0.7 Volt output (average current perslab), a 1.3 Volt input, and 0.7 Volt to 1.2 Volt output range. Thesimulated decoupling capacitance was equivalent to about 0.5 μF at 26 A,assuming 16 phases scaled to the simulated 5 A current at 0.7Volt (worstcase estimation). Also assumed was a 20 mV drop at peak inductor currenton the transistors Q1 and Q2, and the same drop was assumed forvias/wires. The calculated slab inductor value and loss for 90%efficiency were assumed.

In practice two or more of the Buck regulator circuits 50 can beprovided, e.g., four or eight or sixteen, with their operations beingphased and their outputs connected in parallel to supply a single load,e.g., a single processor core, or two or more or loads, e.g., two ormore processor cores and/or other types of circuitry.

FIG. 4 is a chart that summarizes the simulation results for D+E=1 at200 MHz, full output range operation, and a mode where the duty cycle Dwas varied at a constant period T and R_(L). It can be noted that theefficiency exhibited is basically flat over the full output voltagerange of 0.7V to 1.2V and over the output power range of 3.49 W to 10.3W, which is one beneficial result of the use the exemplary embodimentsof this invention.

In the exemplary embodiments of this invention the magnetic shieldinglayer 40 can be fabricated by any suitable conventional metal depositionprocess including, as non-limiting examples, sputtering, electroplatingand electro-less plating.

As for the open slab 10 itself, depending on the specifics of theprocess used and the desired thickness (T), two or more depositions maybe used, such as two 3 μm thick Cu layers that are depositedsequentially one upon another with an intervening layer of some material(e.g., an oxide) as in the embodiment of FIG. 2E. The open slab metal ispreferably copper implemented by a damascene process, though gold,silver and aluminum layers may also be used alone or in combination. Thelayers 10A, 10B are electrically connected together such as by using oneor more vias. In one non-limiting embodiment the two Cu layers 10A, 10Bare electrically connected together at or near their ends (length-wise),although they may be connected also at a point or points between thesetwo end points along the open slab.

In general the total thickness (T) of the slab inductor 10 may be in anexemplary range of about 3 μm to about 15 μm, with about 5 μm to about10 μm being a more preferred range of thickness for many applications ofinterest. The width (W) of the slab inductor 10 may be in an exemplaryrange of about 50 μm to about 300 μm, with about 150 μm to about 250 μmbeing a more preferred range of width for many applications of interest.It is appreciated that the cross-sectional area (T*W) is directlyrelated to the current carrying capacity of the open slab inductor 10and thus also to the realizable value of Q and is determinedaccordingly. The length is selected based primarily on the desired valueof inductance. As a non-limiting example, the length (L) might be in anexemplary range of about 1 mm to about 5 mm, with about possibly 1.5 mmto about 3 mm being a more preferred range of length for manyapplications of interest.

As was noted above, the embodiments of this invention are not limitedfor use in only Buck regulator circuit topologies, as other types ofswitched convertors/regulators (e.g., Boost regulators) can also benefitfrom the use of the teachings of this invention. In general any voltageconverter/regulator containing at least one inductor implemented on asemiconductor chip, such as a chip containing one or more processorcores, may benefit from this invention.

Further, it should be appreciated that the embodiments of this inventionare not limited for use only with providing power to data processorchips and/or only to cores of multi-core processor chips. For example,the embodiments of this invention could be used to provide (possiblyvarying) operating power to integrated circuit chips containing graphicsaccelerator circuitry, or cryptographic circuitry, or communicationscircuitry (e.g., wired or wireless communications circuitry), or tocombinations of these alone or with other types of circuitry and/or incombination with single-core or multi-core data processor circuitry. Invarious embodiments, and by example, at least one Buck regulator 50could supply power to a block of circuitry providing cryptographicfunctionality, while at least one other Buck regulator circuit 50 couldsupply power to at least one core of a single core or a multi-core dataprocessor integrated in the same chip with the block of circuitryproviding cryptographic functionality. In such an exemplary arrangement,and by example, at least one Buck regulator circuit 50 providing powerto the block of circuitry that provides the cryptographic functionalitymay be operated to provide a minimum voltage to the block of circuitryproviding cryptographic functionality when this functionality is notactively being used, while at least one different Buck regulator circuit50 that is arranged to provide power to the at least one processor coremay be operated to provide a maximum voltage to the processor corecircuitry when this functionality is most actively being used,

Further, and as was noted above, it is within the scope of the exemplaryembodiments of this invention to employ a power grid 20 that is designedso as to eliminate or at least reduce an amount of power gridmetallization beneath and closely adjacent to the slab inductor 10. Forexample, and as was previously described, FIG. 1D shows in cross-sectionthe embodiment where the power grid 20 has at least one opening oraperture 20A that is designed to lie beneath the location of the slabinductor 10, thereby eliminating or at least reducing the magneticcoupling between the slab inductor 10 and the power grid 20 and therebyalso beneficially reducing the generation of eddy currents and thenegative effects of the return current on the Q of the slab inductor 10.

As was described above, the embodiment of FIG. 1D illustrates theconcept of having some or all potentially interfering conductors on thechip located sufficiently far away from the slab inductor 10 so that theusage of the magnetic shielding 40 by a dedicated magnetic material mayno longer be required. Since in practice one may not always have theoption of having the aperture window 20A in the power grid 20, theembodiments of this invention also contemplate the use of the magneticshielding layer 40 for shielding the slab inductor 10.

As was also described, FIG. 1E shows a variation of FIG. 1D in which themetal stripes 20B, which form a part of the power grid 20, are locatedorthogonally to the slab inductor 10 (orthogonal to the length axis ofthe slab inductor 10). In this embodiment the aperture 20A is made onlyin those wires of the power grid 20 which are collinear with the lengthaxis of the slab inductor 10, and which are therefore removed from thepower grid 20, leaving present only those wires (20B) of the power grid20 which are orthogonal to the slab inductor 10 (or at least part ofthem). The embodiment of FIG. 1E may for some applications be considereda preferred embodiment of this invention.

While the slab inductor has been described above in reference to asingle or multi-layered structure comprised of copper, and as was notedabove, in other embodiments other metals that exhibit high electricalconductivity can be used such as gold or other metals or combinations ofmetals or metal-containing materials, subject to the practicalities ofselected (e.g., integrated circuit) fabrication processes.

Note again that the embodiments of FIGS. 1D and 1E can be used with anyof the foregoing embodiments. That is, the slab inductor 10 could alsoemploy any of the return current mitigation (and Q enhancing) approachesshown in FIGS. 1C and 2A through 2E.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

As such, various modifications and adaptations may become apparent tothose skilled in the relevant arts in view of the foregoing description,when read in conjunction with the accompanying drawings and the appendedclaims. As but some examples, the use of other similar or equivalentmathematical expressions may be used by those skilled in the art.However, all such and similar modifications of the teachings of thisinvention will still fall within the scope of this invention.

What is claimed is:
 1. A voltage conversion circuit, comprising: aplurality of switches coupled to a voltage source; and a slab inductorhaving a length, a width and a thickness, the slab inductor beingcoupled between the plurality of switches and a load and carrying a loadcurrent during operation of the plurality of switches; where the slabinductor is coupled to the load through a power grid that comprises atleast one conductor, and where the power grid has an aperture madetherein that underlies a location where the slab inductor is disposedabove the power grid.
 2. The voltage conversion circuit as in claim 1,where the power grid is comprised of a plurality of conductors, andwhere the aperture contains only those conductors that are disposedorthogonally to the length of the slab inductor.
 3. The voltageconversion circuit as in claim 1, further comprising a magnetic shieldconfigured to shield the slab inductor from at least one conductorcarrying a return current.
 4. The voltage conversion circuit of claim 3,where the magnetic shield is comprised of a layer of ferromagneticmaterial disposed between the slab inductor and the power grid.
 5. Thevoltage conversion circuit of claim 4, where the slab inductor isembedded within the layer of ferromagnetic material.
 6. The voltageconversion circuit of claim 4, where the magnetic shield is configuredso as to inhibit generation of eddy currents induced by current flowingin the slab inductor.
 7. The voltage conversion circuit of claim 6,where the magnetic shield is configured by being formed as a pluralityof layers.
 8. The voltage conversion circuit of claim 7, where theplurality of layers are disposed in a same horizontal plane locatedbetween a plane defined by the length and width of the slab inductor andthe power grid.
 9. The voltage conversion circuit of claim 7, whereindividual ones of the plurality of layers are disposed one aboveanother in a laminated manner between a plane defined by the length andwidth of the slab inductor and the power grid.
 10. The voltageconversion circuit of claim 7, where some of the plurality of layers aredisposed in a same horizontal plane located between a plane defined bythe length and width of the slab inductor and the power grid, and wheresome of the plurality of layers are disposed one above another in alaminated manner between the plane defined by the length and width ofthe slab inductor and the power grid.
 11. The voltage conversion circuitof claim 3, where the magnetic shield is comprised of a first layer offerromagnetic material disposed between a first lower surface of theslab inductor and the power grid, and is further comprised of a secondlayer of ferromagnetic material disposed above a second upper surface ofthe slab inductor.
 12. The voltage conversion circuit as in claim 1,where the slab inductor is comprised of at least one layer comprised ofcopper and has a total thickness in a range of about 3μm to about 15 μm,a width in a range of about 50 μm to about 300 μm, and a length selecteda function of a desired value of inductance.
 13. The voltage conversioncircuit as in claim 1, where there are a plurality of the voltageconversion circuits each having a respective output connected inparallel to the load.
 14. The voltage conversion circuit as in claim 1,embodied as a buck regulator.
 15. A voltage conversion circuit,comprising: a plurality of switches coupled to a voltage source; a slabinductor having a length, a width and a thickness, the slab inductorbeing coupled between the plurality of switches and a load and carryinga load current during operation of the plurality of switches; and amagnetic shield configured to shield the slab inductor from at least oneconductor carrying a return current.
 16. The voltage conversion circuitas in claim 15, where the slab inductor is coupled to the load through apower grid that comprises the at least one conductor and where themagnetic shield is comprised of a layer of ferromagnetic materialdisposed between the slab inductor and the power grid and is configuredso as to inhibit generation of eddy currents induced by current flowingin the slab inductor.
 17. The voltage conversion circuit of claim 16,where the slab inductor is embedded within the layer of ferromagneticmaterial.
 18. The voltage conversion circuit of claim 16, where themagnetic shield is configured by being formed as a plurality of layers,where the plurality of layers are disposed in a same horizontal planelocated between a plane defined by the length and width of the slabinductor and the power grid.
 19. The voltage conversion circuit of claim18, where at least some of the individual ones of the plurality oflayers are disposed one above another in a laminated manner between aplane defined by the length and width of the slab inductor and the powergrid, and/or where at least some of the plurality of layers are disposedin a same horizontal plane located between a plane defined by the lengthand width of the slab inductor and the power grid.
 20. The voltageconversion circuit of claim 16, where the magnetic shield is comprisedof a first layer of ferromagnetic material disposed between a firstlower surface of the slab inductor and the power grid, and is furthercomprised of a second layer of ferromagnetic material disposed above asecond upper surface of the slab inductor.
 21. The voltage conversioncircuit as in claim 15, where the slab inductor is comprised of at leastone layer comprised of copper and has a total thickness in a range ofabout 3 μm to about 15 μm, a width in a range of about 50 μm to about300 μm, and a length selected a function of a desired value ofinductance, where the voltage conversion circuit is fabricated as partof an integrated circuit, where the load is comprised of at least onecore of a multi-core data processor.
 22. The voltage conversion circuitas in claim 16, where the power grid has an aperture made therein thatunderlies a location where the slab inductor is disposed above the powergrid.
 23. A voltage conversion circuit, comprising: disposed within anintegrated circuit, a plurality of switches coupled to a voltage source;and a slab inductor having a length, a width and a thickness, the slabinductor being coupled between the plurality of switches and a load andcarrying a load current during operation of the plurality of switches.24. The voltage conversion circuit as in claim 23, where the slabinductor is coupled to the load through a power grid, and where thepower grid is configured so as to include beneath the slab inductor onlya conductor or conductors that are disposed orthogonally to a length ofthe slab inductor.
 25. The voltage conversion circuit as in claim 23,further comprising a magnetic shield configured to shield the slabinductor from at least one conductor carrying a return current.